A new analysis of published studies concludes that antioxidant supplements may not provide protection against several cancers -- and could increase the risk of death.
While some experts say the report adds to the growing case against the use of antioxidant supplements, once thought to be widely beneficial in fighting disease and promoting health, others question the researchers' methods and conclusions. They say the supplements have benefits not reflected in this report.
A new study that suggests antioxidants may not protect against several cancers looked only at pills, not at antioxidant vitamins found in foods.
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The findings, published in the Oct. 2 issue of The Lancet, are based on an analysis of 14 randomized trials involving more than 170,000 patients taking antioxidant supplements or placebos. The trials -- about half of which the authors deemed "high quality" by virtue of their design and controls -- reported on patients who developed esophageal, gastric, colorectal, pancreatic or liver cancer.
There is "no convincing evidence that beta carotene, vitamin A, vitamin C and vitamin E or their combinations may prevent gastrointestinal cancers. . . . These antioxidant supplements may even increase mortality," study co-author Goran Bjelakovic, a professor in gastroenterology and hepatology at the University of Nis in Yugoslavia, stated in an e-mail interview.
The analysis looked at antioxidant pills, not at antioxidant vitamins found in foods. Nutrition experts remain in nearly universal agreement that antioxidants found in fresh fruit, vegetables and other whole foods have important benefits. Vitamin-rich whole foods should form the core of a healthy diet, they say.
Some experts said the report sheds new light on an existing concern. "What it does is confirm what we're already learning about antioxidants and heart disease, and that is that they don't provide the protection that we once thought they would," said David Schardt, a nutritionist at the Center for Science in the Public Interest, a Washington-based advocacy group.
Paul Limburg, director of the Mayo Clinic's gastrointestinal neoplasia clinic, said "antioxidants have demonstrated lots of appeal" in other types of research, such as studies based on self-reports of previous supplement use. But data derived from clinical trials -- studies that follow over extended periods people who take either supplements or an inert placebo -- "have been strikingly unremarkable," he said.
Still, Limburg says, the study is not definitive. "It shows, on a best-case scenario, there's no benefit. I think we still need to do further analysis" into the question of harm, Limburg said.
Other experts caution against drawing broad conclusions.
David Forman, a University of Leeds cancer epidemiologist who co-authored an editorial in the same issue of The Lancet, said he "would be very reluctant to draw any conclusions regarding mortality from the evidence that's been presented. What they've got as a result is just on the threshold of being statistically significant."